Amplifiers are devices, which ideally increase the strength of an input signal without appreciably altering the input signal's other signal characteristics. However amplifiers often perform in a manner which is less than ideal. Amplifiers often introduce some distortion of amplitude and phase into the amplified output signal. This is because amplifiers typically contain circuit elements having inherent non-linear characteristics.
In order to reduce unwanted distortions and increase linearity, previous amplifier circuits have made use of linearization techniques, including a linearization technique called feed forward. One such example of a feed forward linearization technique, provides for an input signal which is sampled prior to amplification. A pilot signal is then added to the input signal forming a combined signal. The combined signal is then amplified, which introduces the inherent non-linearities of the amplifier into an amplified combined signal. The sampled input signal is then subtracted from the amplified combined signal to determine the distortion in the sampled amplified signal and an error signal is produced.
The error signal is then adjusted in amplitude and phase, based on the level of the pilot signal detected at the circuit output. The adjusted error signal is then amplified and subtracted from the combined amplified signal to create a circuit output signal having less linear distortion.
In essence the feed forward technique allows the distortion to be introduced into the amplified signal. The magnitude of the distortion is then determined by monitoring the portion of the amplified signal corresponding to the pilot signal. The distortion is then fed back and is subtracted from the amplified signal to cancel itself out. In this way amplifier circuits having reduced linear distortion have been produced.
However, the feed forward technique requires several additional circuit elements including circuitry for producing a pilot signal, circuitry for measuring the level of nonlinear distortion, and circuitry for removing both the distortion and the pilot signal from the amplified signal. Circuit elements that would not be necessary if the amplifier never initially produced the nonlinear distortion. Therefore a method and apparatus for increasing the linearity of the phase and gain of an amplifier circuit, such that the linear distortion in the amplified signal is not initially produced, would be beneficial.